The present invention relates generally to protecting a multiprocessor system from total failure in the case that one processor malfunctions. More particularly, the invention is directed to isolating a malfunctioning processor from the multiprocessor system.
Multiprocessor systems often include more than one interprocessor bus through which the different processors communicate with each other. At least one bus must always be functional for the system to operate properly. If a processor loses power or its power supply malfunctions, its power supplies begin to produce voltages which are not within specification limits. As a result, other malfunctions can occur in a processor. These malfunctions can result in a malfunctioning processor triggering further malfunctions throughout the system. Therefore, the malfunctioning processor must be isolated or "fenced off" from the rest of the system using a fencing circuit.
U.S. Pat. No. 4,356,550 shows a system using a single power supply sensor circuit, capable of operation even after the power supply voltages had dropped. This system was used to provide signals to each of the fencing circuits indicating that the fences should be "raised" so as to isolate the malfunctioning processor from the interprocessor buses.